Line a baking sheet with parchment paper or wax paper. Have a tablespoon or small cookie scoop ready.

In a heavy-bottomed pot, combine the butter, granulated sugar, and cold milk over medium heat. Stir until the butter melts and the sugar dissolves.

Bring the mixture to a full rolling boil and boil for exactly 1 minute while stirring constantly.

Remove the pot from heat and stir in peanut butter and vanilla until smooth.

Add quick oats and fold quickly until every oat is coated.

Drop rounded tablespoons of the mixture onto the prepared parchment, leaving space between cookies.

Let cool at room temperature until firm, about 20-30 minutes.